AUSTIN — The legal sparring between Texas and supporters of a Confederate battle flag license plate has rumbled into its fifth year, even longer than the Civil War.

In the latest volley, the attorney general’s office has turned to the U.S. Supreme Court to help block the flag logo and other unwanted images on government-issued plates.

The state had long held off a Southern heritage group wanting to sell the tags until it sued and won last month in a federal appeals court. Now, the state has asked the Supreme Court to intervene because of conflicting decisions in similar cases across the country.

If they take up the case, the justices will be tackling a raucous freedom-of-speech dispute between the symbol’s backers, who say it honors Confederate veterans, and opponents, who say it’s racially offensive.

At stake: how much power states have in regulating controversial messages on government-issued property.

“The issue is ripe for this court’s resolution,” the attorney general’s office said in an Aug. 7 filing that outlined its arguments against the Sons of Confederate Veterans’ tag.

The group, which has clashed with the state since 2009 over the plate, has until early October to respond. It’s expected to highlight the appeals court’s opinion that the Department of Motor Vehicles engaged in “viewpoint discrimination” when it rejected the proposal.

John McConnell, the group’s attorney, has said that displaying the flag is protected free speech that can’t be restricted simply because it might upset someone.

The 5th Circuit Court of Appeals’ panel in New Orleans, siding with the veterans group, also said the DMV’s standards for what qualifies as offensive were too vague.

“The notion that the Constitution requires states to maintain viewpoint neutrality when deciding whether to issue specialty license plates is unworkable and leads to absurdities,” the state said.

The plate, with the words “Sons of Confederate Veterans 1896” encircling the red battle flag of blue bars and white stars, remains in limbo until the case is resolved.

Nine other states allow it. In seven of them, the Tennessee-based veterans group had to sue to get the plates. Those courts largely declared the emblem private speech that a government cannot restrict.

When it convenes next month, the Supreme Court will sift through nearly 10,000 petitions before picking the 80 to 90 cases it will hear in the session that ends in mid-2015.

Peter Scheer, executive director of the First Amendment Coalition, a California-based advocacy group, said he couldn’t predict if the court will take the Texas case. But he noted it looks for issues that have split lower courts and “cause people on both sides to get elevated blood pressure when they talk about it.”

The DMV has said that because the state manufactures and issues license plates, it should not be forced to put out designs the public opposes.

It received hundreds of comments against the plate. Elected officials, religious leaders, NAACP members and other critics called it a hurtful reminder of slavery.

The veterans group applied for the tag through a procedure separate from Texas’ specialty vendor, My Plates. The group said that the plate commemorates Confederate soldiers and that it would use the proceeds to fund memorial projects.

AT A GLANCE/Fight over license plates

Yes, then no: In 2009, a state Transportation Department advisory group voted in favor of the battle flag plate sought by the Sons of Confederate Veterans. Other agency officials didn't accept that, concerned about the uproar it had caused in other states. Without publicly disclosing the first vote, department leaders sent the proposal back to the advisory group. This time, it failed.

New agency, same outcome: The newly created Department of Motor Vehicles took over license plate approval duties in late 2009. Two years later, when the Confederate plate sponsors renewed their request, the DMV board deadlocked on a 4-4 vote. In November 2011, it unanimously rejected the plate, 8-0.

Turning to the courts: The veterans group in December 2011 sued the DMV in federal court. U.S. District Judge Sam Sparks in April 2013 said the state had authority to reject offensive designs. The group then took the case to the 5th Circuit Court of Appeals in New Orleans, which in July upheld its suit.

Next step: The appeals court ruling means the state would have to allow the plate. That’s now on hold as the state attorney general’s office, representing the DMV, has asked the U.S. Supreme Court to intervene in the case.